Did something happen to the badge that came with your Audax, Anto, or are you looking to fit the old-style stainless badge?
If the latter, I'm afraid you're out of luck. Those were silver-soldered to the frame at time of manufacture when Thorn had its own on-site framebuilding shop.
The more recent badges are stick-ons, but several cuts above the usual variety and far nicer than just a decal. If yours has become damaged, perhaps a call to SJS Cycles would turn up a solution of some kind.
Best,
Dan.